3-Pentenenitrile (3PN) is an important intermediate in the production of adiponitrile (ADN). ADN is of particular interest because it is a commercially versatile and important intermediate in the industrial production of nylon polyamides useful in forming films, fibers, and molded articles.
It is well known in the art that 3PN may be formed through a series of reactions as illustrated in Equations 1 and 2 below,
wherein BD is 1,3-butadiene, HCN is hydrogen cyanide, and 2M3BN is the BD hydrocyanation co-product 2-methyl-3-butenenitrile. U.S. Pat. No. 3,496,215 describes the catalytic hydrocyanation of BD (equation 1) in the presence of NiL4 complexes wherein L is a monodentate phosphorus-containing ligand. The relative amounts of 3PN and 2M3BN can be dependent upon the catalyst utilized in this chemical reaction. U.S. Pat. No. 3,536,748 describes the catalytic isomerization of 2M3BN to 3PN (equation 2) in the presence of NiL4 complexes.
U.S. Pat. No. 3,536,748 discloses that in the presence of HCN, the nickel complex preferentially catalyzes formation of undesired, six-carbon, saturated dinitrile (2-methylglutaronitrile, MGN) from 2M3BN (see Equation 3 below). This patent notes that, because of the overriding competitive hydrocyanation reaction, for the isomerization of 2M3BN to 3PN it is necessary to avoid the presence of large amounts of HCN, for example any amount of the order of or in excess of 1:1 mole ratio with the 2M3BN starting material. The reference further discloses that HCN has no significant effect per se on the isomerization reaction, its presence in minor amounts in the starting material can be tolerated if necessary, and the isomerization process is preferably conducted in the absence of HCN.

U.S. Pat. No. 6,169,198 discloses that hydrocyanation of BD to prepare ADN can generally be divided into three steps. The first is synthesis of mononitriles by hydrocyanation of BD (as in Equation 1 above), for which the selectivity for the linear 3PN is about 70% or less, depending on the catalyst used. The second is isomerization of the 2M3BN present in the mixtures to 3PN (as in Equation 2 above) and isomerization of 3PN to various linear pentenenitriles; the third is synthesis of dinitriles. Also disclosed is a preferred embodiment in which the ratio of the amounts of 3PN to 2M3BN obtained in the monoaddition of HCN onto the BD-containing hydrocarbon mixture is at least 5:1, preferably at least 10:1, in particular at least 20:1, with a catalyst comprising at least one metallocene-phosphorus(III)-nickel(0) complex. The reference further discloses that it is generally possible to dispense with division of the process for preparing ADN into the three steps of monoaddition of HCN onto a BD-containing hydrocarbon mixture; isomerization; addition of HCN onto 4-pentenenitrile (4PN) formed in situ; and the addition of 2 mole equivalents of HCN onto a BD-containing hydrocarbon mixture can be designed as a one-stage process.
In recent years, a new class of catalysts has been described for the transformations of Equations 1 and 2. U.S. Pat. Nos. 5,512,695; 5,512,696; 5,523,453; 5,663,369; 5,688,986; 5,693,843; 5,723,641; 5,821,378; 5,959,135; 5,981,772; 6,020,516; 6,127,567; 6,171,996; 6,171,997; and WO99/52632 describe the use of diphosphite and diphosphinite nickel complexes as catalysts for the hydrocyanation of BD or 3PN and the isomerization of 2M3BN to 3PN. In general, this class of catalysts is characterized by greater catalytic activity and resistance to HCN-derived degradation reactions compared to the catalysts comprising nickel complexes of monodentate phosphites and phosphinites. As a result, this new class of catalysts may generally be used effectively at much lower concentrations and over a broader range of reaction conditions. U.S. Pat. Nos. 5,821,378; 5,981,772 and 6,020,516 describe the capability of a limited number of these catalyst systems to isomerize 2M3BN at the same temperature at which BD is hydrocyanated and disclose improved processes for liquid phase hydrocyanation of diolefinic compounds and subsequent isomerization of the resulting nonconjugated 2-alkyl-3-monoalkenenitriles.
A high yield process for the production of 3PN in which BD hydrocyanation and 2M3BN isomerization occur concurrently in the same reaction zone would be desirable because such a process would require fewer reaction and process separation steps (and the associated equipment and operating costs) than a 3PN production process in which the hydrocyanation and isomerization reactions were performed, for example, in separate reaction zones under reaction conditions optimized independently for BD hydrocyanation to 3PN or for 2M3BN isomerization to 3PN. A 3PN process integrated with a pentenenitrile refining process would be advantageous in that the integration of the refining steps with the concurrent BD hydrocyanation/2M3BN isomerization, and a reaction mixture wherein the 2M3BN concentration is maintained below about 15 weight percent of the total mass of the reaction mixture, would facilitate overall process simplification and could provide reduced capital investment and reduced cost of manufacture, as compared to a 3PN production process in which BD hydrocyanation and 2M3BN isomerization were not performed concurrently in the same reaction zone. Process simplification could be achieved, for example, through elimination of a dedicated 2M3BN isomerization reactor (in which no concurrent BD hydrocyanation was performed) or elimination of at least one distillation column, or both. Recycle of at least a portion of any unreacted BD to the BD hydrocyanation/2M3BN isomerization reaction zone could improve 3PN yield based on BD. Reduced yield loss to undesired by-products, such as MGN and compounds derived from BD dimerization and/or oligomerization, might also be realized with a combined BD hydrocyanation/2M3BN isomerization process integrated with a pentenenitrile refining process.